The present invention relates generally to semiconductor editing, and in particular, to a method and system for dry etching copper features embedded within an organic layer.
Current processes for integrated circuit (IC) editing primarily rely on the use of a Focused Ion Beam (FIB) tool for spatially localized removal, deposition and editing of semiconductor materials. These FIB tools use a liquid metal ion source, typically gallium (Ga+), from which highly energetic beams are formed and focused onto the sample surface by electrostatic lenses. However, exposure to these highly energetic ion beams often causes IC surface damage, gallium contamination, and physical sputtering of the sample surface, which in turn, leads to the undesirable redeposition of sputtered material onto adjacent IC areas causing the circuit to short.
Additional problems have been presented in IC editing using FIB tools with the introduction of copper features for interconnect metallization, as well as with the introduction of organic-based materials to form circuits having inter-level dielectric (ILD) layers. A significant problem with copper features has been the undesired redeposition of sputtered copper as a result of insufficient ion beam compatible chemistries not completely volatilizing these copper etch byproducts. Further, exposure of organic-based layers to the highly energetic ion beams causes these organic layers to become more conductive by forming graphite surface layers and causing electrical leakage between metal features.
Gas-assisted etch (GAE) techniques have also been introduced to reduce or eliminate the above problems associated with FIB processing techniques, including, improving volatilization of by-products and removal of damaged ILD surface layers. In so doing, GAE chemistries, with the assistance of an ion beam, react with the organic layers to form volatile or non-conductive by-products. However, these GAE chemistries are often not reactive enough and show limited utility in both deep-hole FIB processing techniques as well as in editing metal features embedded within organic layers, and in particular, in editing copper features embedded within an organic layer.
Further, as it is desirable in gas-assisted FIB processing to maintain a gas-rich environment in the area being edited, it is standard practice to run these gas-assisted FIB processes for a minimum amount of time. It is believed that it is counter intuitive to have a gas-assisted FIB process run too long as the longer the process runs, the more gas-depleted the area becomes and thus the less efficient the milling process. Accordingly, increasing the duration of exposing a metal feature to a gas-assisted FIB process past conventional exposure times is avoided.
For example, standard practice for editing copper features embedded within an organic layer is to run a gas-assisted FIB XeF2 mill dwell for 1 millisecond at a gas pressure of 2 Torr (BT setting of 2) to maintain a gas-rich environment during the milling process, therein avoiding increasing the dwell time beyond 1 millisecond. Further, running these standard gas-assisted FIB techniques requires a two-step process whereby the organic feature is first milled at standard milling settings and then the standard default milling settings are used to mill the copper feature in the absence gas, or alternatively, the copper is milled using water. However, running these standard two-step gas-assisted FIB techniques, at a minimum amount of time, often provides inconsistent and inadequate editing of metal features within organic layers, particularly, modern metal features having smaller dimensions. They are also hard to control because of the fast milling rates, ineffective in deep holes and permit redeposition of byproducts of the edited metal feature. More global processes used to edit copper features within organic layers include wet etching and plasma/RIE processes. However, it has been found that these processes lead to localization and reaction termination difficulties. For instance, plasma/RIE processes cannot easily etch small areas (<1 square micron in width) without implementing masking materials, such as a photoresist. Additionally, the wet and plasma/RIE processes have a wide range of etch rates that are dependent on both the instrumentation and chemicals used during such processes. These variables make it extremely difficult to “turn-off” the reaction at the exact moment that all material has been removed. The plasma/RIE processes also undesirably may destroy small defects on the IC before such defects can be located and edited, thus, making it very difficult to edit metal features, particularly copper features, that are deeply embedded within an organic layer.
Accordingly, as conventional methods are not consistent or reliable for editing metal features, and in particular smaller (i.e., <1 square micron in width) copper features within organic layers, a need continues to exist in the art for methods that are capable of cleanly and reliably editing such copper features embedded in organic layers without creating any surface damage, contamination and re-deposition of the sputtered material onto other areas of the substrate.